The present invention relates to a method for manufacturing white light-emitting diodes using epoxy resin powder mixed with a fluorescent material adapted to convert a wavelength of white light into a wavelength of blue light emitted from a blue light-emitting diode.
Generally, a white light-emitting diode (LED) is manufactured by placing a liquid resin, mixed with a fluorescent dye, over a blue LED in an encapsulated state. Here, white light has light components uniformly distributed in a wavelength range from 400 nm to 600 nm. Blue light generated by a combination of red, green and blue lights reacts with fluorescent substances respectively emitting red and green lights, thereby exhibiting red and green colors. Lights of these red and green colors are then combined with the blue light transmitted without reacting with the fluorescent substances, thereby causing the human eye to finally view white color.
Referring to FIGS. 3 to 7, diverse structures of LEDs emitting white light (white LEDs) are illustrated which are manufactured in accordance with diverse conventional methods, respectively. That is, such white LED structures may be manufactured using a method involving the steps of attaching a blue LED chip on a printed circuit board (PCB) or a lead frame made of aluminum, potting the blue LED chip with a fluorescent dye, encapsulating the potted chip in accordance with a transfer molding process, and dicing the resulting structure into individual products, a method involving the steps of potting a plastic mold having a desired shape with a fluorescent dye by use of a dispenser, and encapsulating the resulting structure using epoxy, or a method involving the steps of potting a lead frame with a fluorescent dye, and molding the resulting structure using a mold cup having a lamp shape, thereby forming an LED lamp.
Generally, such white LEDs are applied to back illumination for liquid crystal displays (LCDs) and displays for electric home appliances and industrial appliances. Recently, the application of white LEDs has been extended to back illumination for LCDs used in portable electronic products having a light-weight, slim, simple, and miniaturized structure, such as portable radio communication units(i.e cellular phone), and LCDs used in vehicles, in pace with development of associated techniques and diverse demands of consumers. For this reason, white LEDs have been required to have a reduced size. However, known methods of manufacturing white LEDs have a limitation in reducing the size of those white LEDs. Furthermore, there is a problem in that the yield of products having a desired quality or higher is degraded. In addition, the amount of the fluorescent material coated on the chip may be non-uniform. This may result in a severe color deviation among products. There may also be an increase in the processing time taken in the manufacture of products, and an increase in the manufacturing costs.
Therefore, an object of the invention is to provide a method for manufacturing white LEDs, which involves the steps of mixing a fluorescent dye with molding compound powder such as resin powder, compressing the mixture, thereby producing a molding compound compact, and transfer-molding the molding compound compact on a blue LED chip, thereby being capable of forming a white LED serving to convert blue light emitted from the blue LED chip into white light, thereby emitting the white light, while eliminating the potting process used in conventional cases, thereby allowing the white LED to have a slim structure suitable for back illumination for LCDs and other displays used in electronic products having a light-weight, slim, simple, and miniaturized structure, simplifying the manufacturing process to reduce the manufacturing costs and the time taken in manufacturing the white LED, and achieving a considerable improvement in the yield of products having a desired quality.
In accordance with the present invention, this object is accomplished by providing a method for manufacturing white light-emitting diodes adapted to convert a blue light emitted from blue light-emitting diode chips into white light using a fluorescent dye, each of the blue-light emitting diode chips being mounted on a printed circuit board or a lead frame while being bonded to the printed circuit board or the lead frame by a conductive or non-conductive adhesive and having electrodes electrically connected with a circuit pattern plated on the printed circuit board or the lead frame, comprising the steps of: mixing the fluorescent dye with molding compound powder, thereby preparing a mixture; subjecting the mixture to a desired temperature and a desired pressure, thereby shaping the mixture to have a desired shape (for example, a tablet shape); simultaneously transfer-molding the shaped mixture on the blue-light emitting diode chips, thereby forming a molded product; and dicing the molded product into individual white light-emitting diodes using, for example, a dicer. Thus, white light-emitting diodes (white LEDs) are provided which convert a wavelength of white light into a wavelength of blue light emitted from a blue light-emitting diode, thereby emitting white light. The white LEDs manufactured by the method of the present invention can easily and inexpensively emit white light of a high quality, as compared to white LEDs manufactured using a fluorescent dye mixed with a liquid epoxy resin.